The constant free-fall acceleration used to be “explained” by the inertial mass being equal to the gravitational mass, which was, of course, a mystery in itself. It took General Relativity to show that only one type of mass is needed. Specifically, gravity is not really a force (but a spacetime curvature), and the Newton’s second law Fgrav=ma for gravity is only an approximation, valid for not very heavy and not very fast objects.
“Because GR” is a less mysterious answer (thanks, Jack) than the previous model (Newton’s universal gravitation), because it makes better predictions, but the mystery is still there: why does matter curve spacetime?
The constant free-fall acceleration used to be “explained” by the inertial mass being equal to the gravitational mass, which was, of course, a mystery in itself. It took General Relativity to show that only one type of mass is needed. Specifically, gravity is not really a force (but a spacetime curvature), and the Newton’s second law Fgrav=ma for gravity is only an approximation, valid for not very heavy and not very fast objects.
“Because GR” is a less mysterious answer (thanks, Jack) than the previous model (Newton’s universal gravitation), because it makes better predictions, but the mystery is still there: why does matter curve spacetime?